If I download two modpacks for minecraft 1.8 will they merge together?

I'm having trouble dowloading the crazycraft 3.0 but i only want the two best mods in the modpack. So I was wondering if I could download two modpacks and merge them together like they are in Crazy Craft 3.0? (If you can help me on downloading crazycraft 3.0 from the voidswrath launcher my problem is when I click play on the voidswrath launcher it says could not create Java Virtual Machine a fatal exception has occurred the program will exit.